1. Field of the Invention
The present invention relates to coding and decoding methods and packetizing and depacketizing methods, and more particularly, to a method of encoding and decoding and packetizing and depacketizing multimedia data including video data in a wireless transmitting system or in a wireless receiving system.
2. Description of the Related Art
A wireless transmitting device and a wireless receiving device of a wireless code division multiple access (CDMA) system includes a plurality of layers as shown in FIG. 1. A user layer is an application layer. The standards associated with the user layer are codec-related standards such as IS-95, H.324M, H.323 and T. 120. A physical layer, which performs channel coding, PN spreading and modulation, includes a layer where air interfacing is performed. A media access control (MAC) layer or a MUX_sublayer has a signaling portion and includes a radio link protocol (RLP) layer or a radio link control (RLC) protocol layer, where a payload received from a radio path is converted into an input format used in the physical layer. Among the three layers, the physical layer is realized in hardware, so becomes less flexible since it has been determined by the standard. However, the user layer can provide flexibility in terms of its network-independent characteristics.
FIG. 2 is a block diagram for explaining framing performed in an RLP layer. If there are N applications such as a first application, a second application, . . . and an N-th application, N RLPs, that is, a first RLP layer, a second RLP layer, . . . , and an N-th RLP layer are provided. The RLP layers are connected to a physical layer via a MUX and QoS (Quality of Service) sublayer. FIG. 3 illustrates the formation of a service data unit (SDU) for the physical layer, and is performed in the RLP layer. In this process, a packet data unit (PDU) of an application layer (for example, an H.223 MUX_PDU in the case of an H.323M standard, and a packet data unit for H.225 in the case of an H.233 standard) is rarely completely aligned within a 5, 10 or 20 msec window without insertion of overhead. Accordingly, there are three cases shown in FIGS. 4A through 4C.
FIG. 4A refers to a case where an application layer data unit (PDU) is aligned within a physical layer SDU. Referring to FIG. 4A, in this case, overhead may be increased due to the excessive number of fill bits. FIG. 4B refers to a case where two or more application layer data units (PDUs) are aligned within a physical layer SDU. In this case, if synchronization points or the information on the length of a data unit (PDU) of an application layer is damaged, detection of the synchronization point for the second or consecutive application layer data units (PDUs) in the physical layer SDU is not guaranteed. FIG. 4C refers to a case where a data unit (PDU) of an application layer is aligned within two or more physical layer SDUs. In this case, it is not known in which portion the data unit (PDU) of an application layer is segmented.
FIG. 5 shows the structure of an RLP frame to explain problems caused upon RLP framing. In the RLP frame structure shown in FIG. 5, the overall length of a payload including an information field is variable. For example, if the information field is not completely filled with information bits, the empty portion of the information field and the remaining empty portion of the RLP frame are filled with fill bits. Thus, the total length of an RLP frame is fixed. However, if the length field is damaged, the exact length of the information field cannot be ascertained, thus generating serious errors.